Many conventional chemical processes yield process waste streams comprising sulfuric acid, organic tertiary amines, and solvents. The organic tertiary amines are commercially valuable and, as a consequence, it is desirable to recover the tertiary amines from the sulfuric acid. In addition, the waste sulfuric acid may be converted to ammonium sulfate, which may be used, for example, in the fertilizer industry. Also, the solvents that remain may be recovered and/or re-used.
DE 101 46 689 teaches one exemplary method that utilizes distillation to recover organic amines from catalyst waste stream that contains amines. DE 35 22 470 A discloses the recovery of amine and metallic components in a polyphenylene ether synthesis waste stream via the use of a caustic soda. DE 44 16 571 discloses the recovery of amines from acidic stream by the addition of alkali bases followed by distillation until dry.
In addition, CN 1883790 describes the recovery of amines by neutralization with inorganic bases of oxide origin, e.g., NaOH, KOH, Ca(OH)2, or CaCO3. In this method, the sulfates that are created in side reactions must either be disposed of or processed using large amounts of energy, e.g., evaporation or drying, in order to obtain a usable product. Also, due to the molar masses of the oxide used in the reaction, the bases are often used in high amounts. In case of calcium bases, the calcium sulfate that is created precipitates during the reaction and, as such, the suspension must either be diluted or thoroughly blended, which adds to the separation cost.
Typically, when utilized as a fertilizer, an ammonium sulfate composition should comprise a low total amount of organic compounds (“TOC”). DE 35 45 196 A1 discloses the use of ammonia in a process to recover 1.) tertiary aliphatic amines, and 2.) ammonium sulfate from waste sulfuric acid. The yield of the tertiary amines recovered by this process, however, is low and, as a consequence, the TOC remaining in the ammonium sulfate is too high. Thus, this process requires further purification to reduce the TOC in the dry ammonium sulfate to an acceptable level. In addition to keeping TOC at a minimum, it is also important to keep the amount of organic tertiary amine in the ammonium sulfate composition as low as possible. The TOC may be determined according to standard method DIN EN 1484-113.
In other conventional processes, ammonia may be utilized as the inorganic base to treat the process stream. In these processes, however, all of the ammonia that is fed to the recovery process may not react, thus resulting in unreacted ammonia. This unreacted ammonia is problematic from efficiency and environmental perspectives. Specifically, the unreacted ammonia in the treated stream may have detrimental effects on the ability to further separate impurities from the solvents.
Thus, even though conventional processes may treat the sulfuric acid-containing process streams with inorganic bases such as ammonia to recover tertiary amines and to produce ammonium sulfate, the need remains for an improved process that provides for more efficient recovery of the solvents in the treated stream.
All of the references discussed above are hereby incorporated by reference.